Do the rigs all three do it with the same guitars? And do these rigs travel, and if so, does the hum happen everywhere or just certain locations?
Noww, strap on a guitar that hums like this. STand there and listen to the hum. Now turn 90 degrees and face sideways, in other words aim the guitar to the side. Does the hum stay teh same or does it get stronger or weaker. We want to find if the guitar direction matters. It may be environmental.
HAve we recently added light dimmers or something? ANy other electrical changes?